Powder cloud generator and method

ABSTRACT

A powder cloud generator utilized for the development of electrostatic latent images on a receptor and having a chamber with an opening therein to receive the receptor. A selected amount of developer powder is delivered to a specific location within the chamber followed by directing a stream of gas against the powder whereby the powder particles are dispersed and a powder cloud is thereby formed in the chamber. Additionally, means may be provided for electrostatically charging the powder particles with a charge of a desired polarity.

United States Patent 6 1191 Hindell [1'11 -3,774,573 [4 1 Nov. '27, 1973 54] PownEn CLOUD CENERATOR AND; 1 METHOD;

, Inventor: 'Sidney E. Hindell, San Diego,

Calif. Assignee: Diagnostic Instruments, Inc., v San Diego, Calif. 22 Filed: June 30, 1971 [21] Appl. No.: 158,289.

[52 US. Cl 118/629, 1l7/DIG. 6, 118/DIG. 5,

118/621, 118/637, 317/3 7 [51] Int. CL... B05 5/02 [58] Field of Search 118/621, 624, 627,

118/629, 637, 309, 400.5; 117/17, 17.5, DIG. 6, 93.4 R; 317/3 [56] References Cited UNITED STATES PATENTS 3,295,440 1/1967 Rarey'etal. ..101/114 3,133,833 5/1964 Giaimo,Jr... 1181637 2,932,278 4/1960 8166,11. 118/637 3,294,017 12/1966 St. John 101/114 12/19 67 Donalies..'...,..'.,.... 118/637 2,861,543 11/1958 I Crumrine et aL, 118/637 3,336,903

8/1967 Point 1 18/624 Primary Examiner-Mervin Stein Assistant ExaminerLeo Millstein Attorney-Edward Sokolski p 57 7 ABSTRACT A powder cloud generator utilized for the development of electrostaticlatent images on a receptor and 6 having a chamber with an opening therein to receive the receptor. A selected amount of developer powder is'delivered to a specific location within the chamber followed by directing a stream of against the powder'whereby the powder particles are dispersed-and a powder cloud is thereby formed in the chamber. Addi- -tionally, means maybe provided for electrostatically charging the powder particles with a charge of a desired polarity,

' 2 Claims, 2 Drawing Figures PAIEmEnnnvzv-lm 31774 57 INVENTOR SIDNEY E. HINDELL BY SOKOLSKI 8i WOHLGEMUTH ATTORNEYS 1 POWDER CLOUD GENERATOR AND METHOD BACKGROUND OF THE INVENTION tacted with a cloud of charged power particles. If the charged particles have the same polarity as the charges of the latent image, the powder particles will precipitate on the uncharged areas and be repelled by the latent charges. S uchan image is referred to as a negative image. Alternatively, if the powder particles have a charge of an opposite polarity from the latent charge, they will, of course, be attracted to the latent image directly and thus form a positive image. Thus, one can form either a positive or a negative image, depending uponthe charge of the powder particles relative to the charge of the-latent image. For optimum development of such images they must be exposed to or contacted by a uniform distributionof uniformly charged developer particles, such as a homgeneous distribution of developer powder inthe form of a cloud of the powder mixed with a suitable gas. Typical prior systems for producing powder clouds for developing electrostatic images are described in S; Pats. Nos. 2,759,450, 2,784,109 and 2,928,575.

In many of the previous systems, a powder cloud or aerosol was initially created at a location remote from the chamber or container in which the latent image was to be developed and the fine powder particles mixed with the gaseous carrier were transferred or carried by conduits or tubes to a developing zone where they contacted the receptor having the latent image thereon. Such apparatus for forming powder'clouds are often referred to'as powder cloud generators. I

Between the powder cloud generator and the area or enclosure where the cloud contacts-the latentimage, the powder cloud particles preferably were electrostaticloud delivered to the latent image on the receptor did not possess the desired uniform charge.

In other instances motor-driven whirling blades 0 brushes'were positioned in the narrow bottom portion of a conical or other tapered wall development chamber and utilized to agitate and distributethe powder throughout the chamber. However, such apparatus did not provide as homogeneous a .cloud density as most, desired. Further, such apparatus is mechanically complicated by the presence of a large motor and associated means for rotating the brush or blades. Additionally, rotating parts tend to wear, which requires periodic replacement thereof including disassembly of the apparatus.

' SUMMARY OF THE INVENTION The present invention overcomes the disadvantages of the prior art and provides improved control of development of the latent image and resolution thereof, in-.

creased economy of toner usage, and simpler and more reliable, apparatus. Other objectsand features will be in part apparent'and in part pointed'out hereinafter. I

Briefly, the present invention includes anenclosed development chamber having an opening therein in which a receptor element having a latent electrostatic charge image is disposed for developing. Means is provided for delivering a selected amount of a developer 7 powder within the chamber which includes means for posited amount of this toner powder dispersing it callycharged' to have; a desired polarity. In suchprior 7 art systems,the developmentzone normally comprised an enclosure having an opening therein where the receptor having a latent image could be placed. During transfer of the gas-powder mixture from the generator to the development zone or area by means of a tube 5 etc., the gas of the powder cloud served additionally as a carrier. The gas-powder mixture was sprayed or delivered under pressure into the development chamber through a nozzle or the like'where the charged'cloud could fill the chamber and contact the receptor having.

a latent image thereon. r v

Such systems had various disadvantages. For example, the lines carrying the toner particles entrained in a pressurized gas orpowder-gasmixture to the develop ment zone had a tendency to clog. Not only did the lines often get clogged, but the nozzle, which meters the powder cloud into the development chamber, also often became clogged and prevented the flow of the aerosol or powder cloud through, the. system in the desired manner. This resulted in a lack of consistent or a latent electrostatic image thereon is disposed or.

within the chamber in the form of a cloud. Preferably between. the body of depositedtoner'andthe main chamber portion there is a grounded fine metal mesh screen. Above the body of toner resting on the platform, there is located a dc. corona discharge device. In this manner, the toner particles are all charged uniformly and of the desired polarity as they are picked up by the incoming gasand directed into the chamber in the form of a charged powder cloud.

BRIEF DESCRIPTION OF THE DRAWINGS FIGQI is across section, with certain internal parts shown in elevation and other elements shown schematically, of powder cloud apparatus of this invention; and

FIG. 2 is a section on line 2 2 of FIG. 1. Corresponding reference characters indicate corresponding parts throughout the several views of the drawings.

DESCRIPTION OF A PREFERRED EMBODIMENT Turning now'to the drawings, indicated generally at i 11 is powder cloud apparatus of this invention which comprises a generally enclosed preferably electrically grounded box or enclosure 13 of aluminum or any other suitable electrically conductive material which 'will notsustain electrostatic charges. Box 13 has an opening 15 in its top surface 17. An image receptor 19 comprising a substrate of an. insulative material having mounted over opening 15. In accordance with the present invention, this apparatus is generally useful for the development of any charged latent image on substrate 19. This substrate may be a xerographic plate having a photoconductive insulating material overlying a conductive backing member. The photoconductive insulating layer has an electrostatic charge formed thereon as a latent image corresponding to the light pattern to which it is exposed. The insulative layer having this latent image is then placed over the opening so that the latent image is exposed to chamber 21 defined by the interior of box 13, and the image is then developed. Alternatively, image receptor19 may be a layer of insulating material such as a plastic sheet or the like which has a latent charge thereon formed as a result of an ionographic process such as that described by K. H. Reiss in Z. Angew. Physik, Vol. 19, p. 1 (1965). Once again, the surface of insulative receptor layer 19 having a latent image is exposed to'the chamber 21 through the opening 15. Thus, it will 'be understood that image receptor 19 may comprise virtually any layer which as a result of any process has an electrostatic latent image formed thereon and which image is susceptible of development.

Secured to a side wall 23 of chamber 13 and extending inwardly to the chamber 21 is aflat, generally horizontal platform 25. Platform 25 is enclosed by side walls-27 and a top wall 29 forming a small compartment surrounding the platform 25, with platform 25 forming the compartment bottom and a small portion of chamber wall 23 forming the rear wall thereof. Projecting downwardly through the compartments top wall 29 is an inlet tube 31 which passes through top surface 17 of the main housing or chamber 13. Inlet tube 31 provides access to deliver a selected amount of powder particles 33 into chamber 21 to come to rest on platform 25. The amount of powder particles 33 deposited on platform 25 will be determined by the geometry of the chamber 21 and the desired density of the powder. cloud to be formed therein. The amount of powder 33 may be manually measured and fed into tube 31. Alternatively, conventional automatic measuring and feeding means may be readily provided to feed the desired amount of the powder for each cycle of development, or for each receptor 19 placed on the device.

The types of powder material utilizable in the present invention are well known in the art. Typical powder materials include charcoal, carbon black and various carbonaceous type pigments. Additionally, finely divided material having pigments added thereto can be 37 disposed adjacent the platform 25 on which rests the body of powder 33. The relative elevations of the outlet end 37 of gas inlet tube 35 and platform 25 above bottom wall 36 of the chamber are such that a desired deposition of powder fines will occur on the receptor 19. In powder cloud development, the objective is to cause large powder particles to fall away from the image receptor, with only fines being carried upward to the latent image. Placing the platform 25 'too close to image receptor 19 can cause impingement of large powder particles on the receptor. If the platform 25 is too far from the image receptor, then thelatent'image will be underdeveloped. However, while there is some latitude in the placement of the gas inlet so as to achieve desirable results, the most desirable location of the. inlet tube is easily and readily determined.

The inner end 37 of the tube 35, which is preferably flattened slightly to improve cloud formation, is disposed adjacent the powder particles 33 to deliver the incoming gas so that it will disperse the powder resting on the platform 25, blowing it into chamber'2l. Preferably, a fine wire mesh screen 39'is provided to break up agglomerations in the powder as it enters the chamber volume 21 when the gas blows'the powder off the platform. The screen 39, which is preferably grounded, can be made of stainless steel, copper or any other metallic conductor. Typical mesh size for screen 39 will range from 150 to 250 mesh in order to properly break up such agglomerations in the powder mass 33. Clogging of the screen can occur if damp powder or a gas with a high moisture content is used. Thus, it is desirable that the screen be removable from the device for cleaning, if required.

The gas entering through the line 35 can be air or any other suitable dry carrier gas. Obviously, air is the most practical and least expensive carrier gas. The gas is admitted under a preset pressure, the duration of gas inlet being controlled by a timer actuated valve 38. A typical range of flow rates of the gaseous material utilized can be from 2.3 to 5.3 cubic feet per-minute. The gasflow rate is controlled by the gas pressure, the length of tube 35, the tubes bore diameter andtemperature. To obtain the above typical flow rates, pressure settings range from3 to l0 psi. Typically, a gas pressure of 4 psi maintained for 10 seconds provided good results. lmage density appears to be relatively independent of the gas inletpressure and duration once minimums have been established to provide complete overall used such as finely-divided resins containing pigments 1 known in the art can be utilized and are herein contemplated. The density of the developed image is controlled in partby the amount of powder used. The volume of the powder used for good development density is dependent on the particular chamber dimensions.

A gas inlet tube 35 extends through chamber wall 23 and terminatesin the small compartment with its end image development. I

Box or housing 13 preferably has an enlarged opening 41 at the bottom thereof. A filter 45 of spun glass or the like covers the opening 41 while a baffle element 46 is spatially disposed above the filter within the chamber. This allows the gas to leave the chamber while filtering out the powder particles. In other words, 1

31 and connected to a suitable high voltage source 49, e.g., up to kv or more. The other terminal of voltage source 49 is preferably-grounded, but it is to be understood the expression grounded as used herein encompasses merely connecting the screen and platform to the voltage source terminal of polarity opposite to that terminal which is connected to electrode 47, and

does not necessarily mean an actual earth ground.

The electrode 47provides the desired corona discharge into the powder cloud formed when the gas from tube 35 causes the powder to be dispersed. The corona discharge is thus formed between a sharp end 51 of the electrode 47 and the grounded wire mesh screen 39. The end of the electrode is located just above the top of the body of powder 33 so that the incoming gas can serve to continuously clean it. Since the powder particles must pass through screen 39, they in turn inherently are moved through the corona discharge and will be charged according to the desired polarity as determined by the polarity of the discharge. The applied high voltage to the electrode 47 as well as t the discharge current'are limited to prevent actual arcelectrically conductive surface connected to screen 39 and the grounded terminal of voltage source 49) preferably has divergent walls 48 positioned on opposite thus, in effect, replace theplatform since the powder would be resting'on the belt surface prior to dispersement. i

In using the above-described apparatus to practice the methods of this invention, a measured amount of powder or toner is delivered to the platform prior to development of each latent image and the powder cloud produced by directing the stream of gas at the powder body is blown directly into chamber 21 with the toner particles uniformly charged at the desired polarity as they pass through the corona discharge. At no time is a mixture of gas and powder moved through a tube or restricted conduit. The powder cloud herein is actually created within the confines of the development chamber. Thus, there is no possibility of clogging of tubes or nozzles and a consistent homogeneous powder cloud is formed. By convenient adjustment of the amount of powder selected, gas pressure and the duration of gas flow, excellent control of development of the latent image and good resolution thereof. are obtained with good toner economy.

sides of powder body 33 as seen in FIG. 2. These walls der has been admitted or introduced into the chamber. 1

Alternatively, of course, a valve can be utilized in place of cap 53 particularly where an automatic feed means is provided. Means thus should be preferably provided for closing the tube 31 at the top thereof so that during the generation of the powder cloud the cloud cannot escape through the tube and affect the performance of the apparatus. Such an automatic continuous powder feed having a belt carrying individual capsules of a pre determined amount of powder may be provided so that as the belt is advanced new'capsules successively are brought into alignment with the gas inlet. Each capsule would then be opened just prior to beginning gas flow for development of a particular image. This belt would In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained.

As various changes could be made in the above apparatus and methods without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

I claim:

1. Powder cloud apparatus comprising:

an enclosed chamber having an opening therein in which an image receptor can be disposed;

means for delivering a selected amount of a developer powder within said chamber;

a generally horizontal platform disposed in said chamber for receiving said powder and allowing the powder to rest thereon;

an electrically-grounded screen disposed adjacent said platform to diffuse the powder as it is blown therefrom by gas from inlet means;

a corona discharge electrode disposed adjacently above said platform whereby a corona discharge I can be generated between said'screen and said,

r 2. Powder cloud apparatus of claim 1 wherein said means for admitting the powder includes a tube, said electrode being mounted within said tube. 

1. Powder cloud apparatus comprising: an enclosed chamber having an opening therein in which an image receptor can be disposed; means for delivering a selected amount of a developer powder within said chamber; a generally horizontal platform disposed in said chamber for receiving said powder and allowing the powder to rest thereon; an electrically-grounded screen disposed adjacent said plAtform to diffuse the powder as it is blown therefrom by gas from inlet means; a corona discharge electrode disposed adjacently above said platform whereby a corona discharge can be generated between said screen and said electrode; and gas inlet means connected to said chamber for introducing a gas burst thereto, this inlet means being positioned to deliver the gas so as to propel the powder from its receiving means and disperse and distribute it as a cloud across the chamber.
 2. Powder cloud apparatus of claim 1 wherein said means for admitting the powder includes a tube, said electrode being mounted within said tube. 